Air travel and air commerce have become virtually indispensable to the economies of the industrialized nations. Many different facets of business, industry, government, and the overall public depend upon goods and services delivered via aircraft. Air transportation has become as common and ubiquitous to the modern world as the rail roads of many decades past. Reflecting their importance to modern commerce, the Federal Aviation Administration (FAA) recently estimated that by the year 1990, there were approximately 265,000 registered general aviation aircraft in the United States alone. In addition to general aviation aircraft, there were approximately 6000 commercial carrier aircraft in use as well. These aircraft made use of 17,500 airports, of which 5200 were in public use. The aviation industry plays an enormous and indispensable role in the national economy and interstate commerce. As such, the safe and efficient use of the national airspace plays an equally important role.
Ensuring the safe and efficient use of the national airspace is a primary objective of the FAA. The FAA is the authority tasked by the government of the United States with promoting the safe, orderly, and expeditious flow of air traffic. As such, the FAA maintains an Air Traffic Control (ATC) organization and system which operates and regulates the national airspace system. ATC system accomplishes many functions in the course of operating and regulating the national airspace system. Such functions include the organization of airspace into routes for departures, en route airways, and arrivals, the maintenance of radio navigation aids, and the like. A primary function ATC provides is air traffic deconfliction and collision avoidance.
With reference now to Prior Art FIG. 1, a diagram 100 of the scheme of operation of the present ATC system is shown. Prior Art FIG. 1 shows an ATC enroute air traffic control center 101, commonly referred to as an ATC center. The ATC center 101 is coupled to a radar system 102. Radar system 102 sweeps a radar beam 103 in a circular pattern in order to detect and track the various aircraft 104-108 enroute through the airspace above.
As is well known, the ATC center 101 contains display systems, computers, and various automation systems, along with air traffic control personnel (e.g., controllers) who are responsible for providing ATC services. ATC center 101 also includes various communication systems which provide ATC voice and data communications interfaces to aircraft 104-108. ATC center 101 utilizes the surveillance data gathered by radar system 102 to obtain the location and heading information regarding the aircraft 104-108. The ATC center 101 is typically linked to radar system 102 via the standard terrestrial telecommunications network.
Radar system 102 sweeps the surrounding airspace with a wide "surveillance beam" of radar energy. The radar beam 103 is emitted from a rotating radar antenna, typically at either 1300 or 2800 MHz, and reflects off of the metal skin of the aircraft within its beam width (e.g., aircraft 105). The various radar reflections and the corresponding azimuths of the radar antenna, as is well known, together provide the range, azimuth, and elevation of the various aircraft within the area swept by the radar beam (i.e., the surveillance volume). By observing the locations of aircraft 105-108 over successive sweeps, the various headings and speeds of aircraft 105-108 can be determined.
Air traffic controllers in ATC center 101 utilize the information provided by radar system 102 to deconflict the flight paths of the various aircraft within the surveillance volume and ensure a safe amount of separation. For example as aircraft 105 flies through the airspace monitored by ATC center 101, ATC center 101 monitors the progress of aircraft 105 and all nearby aircraft to ensure safe separation. Aircraft 105 is in communications contact with ATC center 102 and responds to voice commands from the air traffic controllers to alter course or altitude should the need arise. Hence, to ensure safe air navigation through its monitored surveillance volume, ATC center 101 is required to track the present position and heading of all aircraft within the surveillance volume and each aircraft consequently needs to remain in communications contact with ATC center 101. In addition to relying upon ATC center 101 to ensure safe separation, each individual aircraft (e.g., aircraft 105) is ultimately responsible for maintaining safe separation through visual or any other means.
Thus, even though ATC center 101 provides a technical means of ensuring safe separation between aircraft, each individual aircraft must, in essence, keep an eye out for collisions. Consequently, there are two basic types of flights: those under visual flight rules (VFR) and those under instrument flight rules (IFR). In VFR flights, the aircraft pilot is responsible for separation from all other aircraft by maintaining a constant visual scan of the surrounding sky. No flight through clouds are allowed. VFR flights are thus typically conducted on fair weather days. No contact with an ATC center (e.g., ATC center 101) is required. In IFR flights, aircraft must remain in communications contact with an ATC center (e.g., ATC center 101). IFR flight allows aircraft to penetrate clouds or fly at altitudes above 18,000 ft. Commercial aircraft usually fly above 18,000 ft and thus almost always fly under IFR. When an IFR aircraft is flying through clear weather, the individual aircraft is primarily responsible for ensuring safe separation (e.g., through visual means). When the aircraft is flying through clouds however, the aircraft is completely dependent upon an ATC center for collision avoidance. Hence, while flying through clouds or bad weather, (referred to as instrument meteorological conditions, or IMC) there is currently no visual means of ensuring safe separation and collision avoidance.
Hence, where aircraft 104 is a VFR aircraft and aircraft 105-108 are IFR aircraft, ATC center 101 has an absolute requirement to know the whereabouts of IFR aircraft 105-108, and a strong requirement to know the whereabouts of VFR aircraft 104. The resolution of radar system 102, however is limited. Radar system 102 tends to have relatively good range and azimuth resolution. The elevation resolution, however, is very limited. Radar system 102 cannot accurately determine the altitudes of the aircraft within the surveillance area. As such, each aircraft within the surveillance volume must individually report their altitude to the air traffic controllers of ATC center 101. Additionally, at different times there may be aircraft within the surveillance volume which are not within radar beam 103 as it sweeps around radar system 102 (e.g., aircraft 104), or are otherwise within an area masked from radar system 102 (e.g., masked due to mountainous terrain). These and other such problems have lead to the use of various forms of automatic dependent surveillance systems.
Automatic dependent surveillance (ADS) systems are widely known in the aviation industry (the most common examples being mode 3A and mode C transponder systems). ADS refers to the fact that the surveillance depends upon an aircraft determined position fix from equipment onboard the aircraft. The aircraft determined position is communicated to an ATC center using automated datalink technology. Using the aircraft determined positions, air traffic controllers monitor the progress of aircraft within their surveillance volume, ensure safe separation, and otherwise control air traffic. As ADS systems become more sophisticated and incorporate modern integrated circuit technology, together with the emergence of global positioning system (GPS) satellite based navigation technology, a fully automated world wide aircraft surveillance and collision avoidance system becomes possible.
A GPS based ADS system would include the automatic broadcast of each aircraft's position in a standardized manner on standardized frequencies using standardized data formats. Such a system is often referred to as an ADS-B system, or automatic dependent surveillance broadcast system. The automatic broadcasts would in turn allow any properly equipped aircraft to know the position and heading of all neighboring aircraft. Each aircraft would utilize GPS technology to determine its position and heading. The position and heading would then be transmitted to other ADS-B equipped aircraft. The ADS-B signals would be transmitted using standard transponder technology already present in many aircraft (e.g., mode S). In such an ADS-B system, the transponders aboard each aircraft would respond to interrogation from ground based radar systems (e.g., radar system 102) as they currently do, and also spontaneously transmit the aircraft's GPS determined present position periodically. This process is often referred to as GPS squitter. Each aircraft in the vicinity would receive the GPS squitter and track the position and progress of neighboring aircraft, thus implementing a GPS squitter Traffic Alert and Collision Avoidance System (TCAS).
It should be noted that there have been several studies and publications describing and discussing the use of GPS based ADS-B systems to augment or possibly even replace the radar based surveillance system currently in use in the United States. GPS based ADS-B promises many advantages over the current system. Those desiring additional discussion of GPS based ADS-B and GPS squitter systems should consult "Ronald Braff, J. David Powell, Joseph Dorfler, APPLICATIONS OF THE GPS TO AIR TRAFFIC CONTROL, Global Positioning System: Theory and Applications, Volume II, ISBN 1-56347-107-8", which is incorporated herein as background material. Additionally, those desiring a more detailed discussion of GPS and general aviation should consult "Ralph Eschenbach, GPS APPLICATIONS IN GENERAL AVIATION, Global Positioning System: Theory and Applications, Volume II, ISBN 1-56347-107-8", which is also incorporated herein as background material.
Because GPS squitter TCAS is not dependent upon ground based radar surveillance, the associated terrain masking and radar resolution problems are eliminated. Modern aircraft cockpit avionics often incorporate multi-function display screens capable of conveying a variety of information to the flight crew. GPS squitter TCAS would enable the display of aircraft in the vicinity and allow the aircrew to ensure safe separation even while flying in IMC.
However, many problems remain. Visually scanning the flight path and the surrounding airspace remains the most intuitive means of ensuring safe separation from neighboring aircraft. While flying in IMC, visual means of collision avoidance remain ineffective. Modern cockpit avionics, while capable of efficiently displaying a wide variety of information to the aircrew, are still display based, in that their information is conveyed visually, in a head down manner. To receive the information, the aircrew needs to look down, into the cockpit, at the display, as opposed to looking out of the aircraft in the direction of flight.
In addition, although the GPS squitter information can be readily displayed using the avionics, the instrument display is inherently 2 dimensional (2D) in nature. Neighboring aircraft are typically presented on the instrument display screen using 2D alphanumeric symbology. This requires the aircrew to quickly translate the 2D display symbology into a real world 3 dimensional (3D) range and bearing. The 2D display symbology is translated to a 3D range and bearing, which is utilized for a visual cross check for the real world aircraft represented on the display. The process of looking down into the cockpit at a relatively small 2D instrument display, mentally translating the display symbology into a 3D range and bearing, and looking up at the corresponding range and bearing to find the represented aircraft, is not intuitive. This process leads to the aircrew repeatedly looking down into the cockpit at the display, looking back up outside along the indicated bearing, visually scanning for the aircraft if it isn't immediately seen, looking back down into the cockpit at the display, looking back up and scanning for the represented aircraft, and so on. If the airspace in the immediate vicinity is congested, or if the airspace is partially (or completely) obscured by clouds, the aircrew is soon left depending primarily (if not solely) upon air traffic control personnel to ensure safe separation, regardless of any ADS-B system in use.
Thus, what is required is an aircraft traffic alert and collision avoidance system which has the accuracy and reliability of GPS and is compatible with current flight regimes (e.g., VFR, IFR, and the like). The required system should provide the aircrew with a visual, intuitive means of ensuring aircraft safe separation. The required solution should allow the aircrew to visually cross check air traffic alerts from either GPS squitter avionics or air traffic controller communications. The required solution should be fully functional in differing weather conditions, even in full IMC flight. Additionally, the required solution should be easily interpreted and convey air traffic alert and collision avoidance information while allowing the pilots to remain heads up, visually scanning the airspace outside the cockpit. The system of the present invention provides an elegant solution to the above requirements.